In a medium bowl, combine graham cracker crumbs and sugar, then stir in the melted butter until the mixture resembles wet sand. Press into a 9-inch pie dish and freeze for 15 minutes.

In a large mixing bowl, whip the heavy cream with a hand mixer on high speed until stiff peaks form, about 3–5 minutes.

In another bowl, blend the softened cream cheese and sweetened condensed milk until smooth. Add lemon zest, key lime zest, vanilla extract, sour cream, and both lemon and key lime juices; mix until fully incorporated.

Gently fold the whipped cream into the filling mixture with a silicone spatula until no visible streaks remain.

Pour the filling into your chilled crust, smoothing it out with a spatula. Refrigerate for at least 2 hours to set completely.

Optional: Whip additional cream to a soft peak and spread it over the chilled pie once it's set. Garnish with fresh lemon and lime slices.